[Practice] Merge two binary trees

[lpatmo]

https://leetcode.com/problems/merge-two-binary-trees/submissions/

[lpatmo]

var mergeTrees = function(t1, t2) {
    //if both trees have no children, return sum of root nodes
    if (t1 && !t2) { return t1; }
    if (!t1 && t2) { return t2; }
    if (!t1 && !t2) { return null; }
    
    t1.val += t2.val;
    t1.left = mergeTrees(t1.left, t2.left);
    t1.right = mergeTrees(t1.right, t2.right);
    return t1;
    
};